WO1999051338A1

WO1999051338A1 - Multi-metal oxide compounds

Info

Publication number: WO1999051338A1
Application number: PCT/EP1999/002082
Authority: WO
Inventors: Hartmut Hibst; Frank Rosowski
Original assignee: Basf Aktiengesellschaft
Priority date: 1998-04-06
Filing date: 1999-03-26
Publication date: 1999-10-14
Also published as: DE19815279A1

Abstract

The invention relates to multi-metal oxide compounds with a 2-component structure, containing molybdenum, hydrogen, one or more of the elements phosphor, arsenic, boron, germanium and silicon, one or more of the elements copper, zinc, cobalt and iron, and the element antimony. The invention also relates to the use of said compounds for producing methacrylic acid by means of a gas phase catalytic oxidation process.

Description

Multimetal oxide materials

description

The present invention relates to multimetal oxide compositions of the general formula I.

[A] _p [B] _q (I),

in which the variables have the following meaning:

A = MO12 Xa b Xc Xd S _e xl O _x ,

B = Xi Sb _g H _h O _y

X ¹ = phosphorus, arsenic, boron, germanium, and / or silicon, preferably phosphorus,

X ² = vanadium, niobium, tungsten, rhenium and / or rhodium, preferably vanadium and / or tungsten,

X ³ = lithium, sodium, potassium, rubidium, cesium, silver and / or copper, preferably cesium and / or copper,

X ⁴ = antimony and / or bismuth, preferably antimony,

X ⁵ = hydrogen and / or NH ₄ ®,

X ⁶ = copper, zinc, cobalt, iron, cadmium, manganese, magnesium, calcium, strontium and / or barium, preferably copper,

a = 1 to 6, preferably 1 to 3,

b = 0 to 6, preferably 0.2 to 4 and particularly preferably 0.5 to 2.5,

c = 0 to 5, preferably 1 to 3,

d = 0 to 6, preferably 0 to 3 and particularly preferably 0 to 1.5,

e = 0 to 3, preferably 0 to 1, 2 f = 0 to 20, preferably 0 to 10 and particularly preferably 0 to 5,

g = 0.1 to 50, preferably 0.2 to 20 and particularly preferably 0.2 to 5,

h = 0 to 50, preferably 0 to 20 and particularly preferably 0 to 12,

x, y = numbers that are determined by the valency and frequency of the elements other than oxygen in (I)

and

p, q = non-zero numbers whose ratio p / q is 1: 0.01 to 1: 5, preferably 1: 0.02 to 1: 3 and particularly preferably 1: 0.04 to 1: 2,

which the portion [A] _p in the form of three-dimensionally extended areas A of the chemical composition

A: M012 Xa Xb _C d S _e X ^ O _x

and the proportion [B] _q in the form of three-dimensionally extended regions B of the chemical composition

6

B: Xi Sb _g H _h O _y

included, the areas A, B being distributed relative to one another as in a finely divided mixture of A and B, with the proviso that at least one separately formed oxometalate B

6

X _l Sb _g H _h O _y

is used, which is obtainable by preparing a dry mixture from suitable sources of the elemental constituents of oxometalate B, which contain at least part of the antimony in the oxidation state +5, and this at temperatures of 200 to 1200 ° C., preferably Calcined 200 to 850 ° C and particularly preferably 500 to 850 ° C. 3

In addition, the present invention relates to processes for the preparation of multimetal oxide materials (I) and their use as catalysts for the gas-phase catalytic oxidation of methacrylic acid to methacrylic acid.

EP-A 668103 relates to multi-component multimetal oxide compositions, the gross composition of which and the component composition of the components corresponds to that of the multimetal oxide compositions (I) according to the invention. These multimetal oxide materials are described in EP-A 668103 and others. recommended as catalysts for the gas phase catalytic oxidative production of methacrylic acid from methacrolein. A disadvantage of the multimetal oxide compositions of the prior art, however, is that both their activity and the selectivity of methacrylic acid formation are not fully satisfactory for a given conversion.

The object of the present invention was therefore to provide multimetal oxide compositions which do not have the disadvantages of the multimetal oxide compositions of the prior art. Accordingly, the multimetal oxide materials (I) defined at the outset were found.

EP-A 835, DE-C 3 338 380, DE-A 4 220 859 and DE-A 4 307 381 also relate to multi-component multimetal oxide compositions which are suitable as catalysts for the gas-phase catalytic oxidative production of methacrylic acid from methacrolein, but the element composition of the components of these multimetal oxide compositions of the prior art is different from that of the inventive multimetal oxide compositions (I).

_According to the invention, it is advantageous if at least one of the two portions [A _Jp , [B] _{q of} the multimetal _{oxide compositions} (I) _according to the invention is contained in the latter in the form of three-dimensionally extended regions of the chemical composition A or B, the large diameter of which d _& or d _B (longest connecting section through the center of gravity of the area of two points located on the surface (interface) of the area) is> 0 to 200 μm, preferably 0.1 to 100 μm. A particularly favorable large diameter range is the range 0.2 to 50 μm and the range 0.2 to 30 μm is particularly advantageous. Of course, the large diameters can also be 0.1 to 150 μm or 75 to 125 μm (the experimental determination of the large diameters allows, for example, microstructure analysis using a scanning electron microscope (SEM)). 4

Both the fraction [A] _p and the fraction [B] _g can be present in the multimetal oxide compositions according to the invention in crystalline and / or amorphous form. This means that both the areas A and the areas B consist essentially of small 5 crystallites, the size of which is typically 0.1 to 10 μm.

Those multimetal oxide materials whose area A consists essentially of crystallites are of particularly favorable nature

10 exist, the structure type of that of the ammonium salt

Molybdatophosphoric acid ((NH) ₃ P0 ₄ (Moθ ₃ ) ι ₂ * 4H ₂ 0) corresponds. The presence of this type of crystal structure can be demonstrated, for example, by the fact that the X-ray diffraction recordings of the multimetal oxide composition (I) according to the invention reflect the diffraction pattern of the ammonium salt

15 contains the molybdatophosphoric acid (fingerprint), with slight differences in the intensities and the position of the diffraction lines being possible, depending on the element composition. The X-ray diffraction fingerprint of the ammonium salt of molybdatophosphoric acid is e.g. published as index card 9-412 of the

20 JCPDS-ICDD card index (1991), which is known to the person skilled in the art and is generally accessible. Another source is Natl.-Bur. Stand. (US), Circ. 539, 810 (1959). If the fraction [A] _p comprises the element antimony, in contrast to the other possible constituents of this fraction, this is often not broken down into the structure type of ammonium

25 salts of crystallites containing molybdate phosphoric acid are installed and are then on the surface of these crystallites or in the interstices. As a rule, it is advantageous if 85 to 95% of its weight is used as antimony to produce the multimetal oxide materials.

30

In particular, those multimetal oxide compositions according to the invention are preferred whose regions B essentially consist of crystallites which have the trirutile structure type of the α- and / or β-copper antimonate CuSb ₂ θ ₆ . α-CuSb ₂ 0 ₆ crystallizes in one

35 tetragonal trirutile structure (E.-O. Giere et al., J. Solid

State Chem. 131 (1997) 263-274), while β-CuSb ₂ 0 _{6 has} a monoclinically distorted trirutile structure (A. Nakua et al., J. Solid State Chem. 91 (1991) 105-112 or comparative diffractogram in Index 17-284 in the 1989 JCPDS-ICDD index). Furthermore

Areas B are preferred which contain the pyrochloric structure of the mineral Partzite, a copper-antimony oxide hydroxide with the variable composition Cu _y Sb _2-2 (0, OH, H ₂ 0) _6-7 (y <2, 0 <x <1) (B. Mason et al., Mineral. Mag. 30 (1953) 100-112 or comparison diagram in index card 7-303 of the JCPDS-ICDD index

45 1996). 5

Furthermore, regions B can consist of crystallites which structure the copper antimonate Cuo, Sb ₄ Oi ₉ (S. Shimada et al., Chem. Lett. 1983, 1875-1876 or S. Shimada et al., Thermochim. Acta 133 (1988) 73-77 or comparative diagram in index card 45-54 of the JCPDS-ICDD index) and / or the structure of CuSb0 ₄ , s (S. Shimada et al., Thermochim. Acta 56 (1982) 73-82 or S Shimada et al., Thermochim. Acta 133 (1988) 73-77 or comparison diagram in index card 36-1106 of the JCPDS-ICDD index).

The multimetal oxide compositions (I) according to the invention are easily e.g. obtainable by first preparing oxometalates B,

6 ^S ι Sbg H _h O _y ,

separately formed as a starting mass 1 in finely divided form. The oxometalates B can be prepared by preparing a preferably intimate, expediently finely divided, dry mixture from suitable sources of their elemental constituents, and this at temperatures of 200 to 1200 ° C., preferably 200 to 850 ° C., particularly preferably 500 to 850 ° C calcined (usually a few minutes to several hours). It is only essential to the invention that at least a part of the oxometalates B of the starting mass 1 (hereinafter this part is called oxometalates B *) can be obtained by the fact that suitable sources of the elemental constituents of the oxometalate B, the least a part of the antimony in the Contain oxidation level +5, a preferably intimate, expediently finely divided, dry mixture is prepared and this is calcined at temperatures of 200 to 1200 ° C, preferably 200 to 850 ° C, particularly preferably 500 to 850 ° C (usually a few minutes to several Hours). The calcination of the precursors of oxometalates B can generally be carried out under inert gas, but also under a mixture of inert gas and oxygen, such as air, or even under pure oxygen. Calcination under a reducing atmosphere is also possible. As a rule, the required calcination time decreases with increasing calcination temperature. The proportion of the oxometalates B * in the finely divided starting mass 1 is advantageously at least 10, better at least 20, often at least 30 or at least 40, preferably at least 50, more preferably at least 60, particularly preferably at least 70 or at least 80, often at least 90 or 95 and very particularly preferably 100% by weight, based on the starting mass 1. Oxometalates B * are obtainable, for example, by the preparation methods described in detail in DE-A 2 407 677. Among these, the procedure is preferred in which antimony trioxide and / or Sb0 ₄ in aqueous 6

Medium oxidized by means of hydrogen peroxide in an amount which is equal to or exceeds the stoichiometric at temperatures between 40 and 100 ° C to antimony (V) oxide hydroxide hydrate, even before this oxidation, during this oxidation 5 and / or after this oxidation aqueous solutions and / or suspensions of suitable starting compounds of the other elemental constituents of oxometallate B * are added, then the resulting aqueous mixture dries (preferably spray-dried (inlet temperature: 250 to 600 ° C., outlet temperature: 80 to

10 130 ° C)) and then calcined the intimate dry mixture as described. In the process as just described can be, for example, aqueous hydrogen peroxide solutions with a H ₂ 0 ₂ content of 5 to 33 weight -.% Or more of use. A subsequent addition of suitable starting compounds of the other elementary contacts

15 stituents of oxometallate B * are particularly recommended if they can catalytically decompose the hydrogen peroxide. Of course, one could also isolate the antimony (V) oxide hydroxide hydrate from the aqueous medium and e.g. dry with suitable fine-particle starting compounds of the other ele-

Mix 20 mental constituents of the oxometalate B * intimately and then calcine this intimate mixture as described. It is essential that the element sources of the oxometalates B, B * are either already oxides, or those compounds which are obtained by heating, if appropriate in the presence

25 of oxygen, can be converted into oxides. In addition to the oxides, halides, nitrates, formates, oxalates, acetates, carbonates and / or hydroxides are therefore particularly suitable as starting compounds (compounds such as NH ₄ OH, NH ₄ CHO ₂ , CH ₃ COOH, NH ₄ CH ₃ CO ₂ or ammonium oxalate to be gasified at the latest during the later calcination

30 permanently escaping connections can disintegrate and / or be decomposed can also be incorporated). In general, the intimate mixing of the starting compounds can also be carried out in dry or wet form for the preparation of oxometalates B. If it is in dry form, the initial

35 compounds expediently used as finely divided powders. However, the intimate mixing is preferably carried out in wet form. Usually, the starting compounds are mixed together in the form of an aqueous solution and / or suspension. After the mixing process is complete, the fluid mass is dried and

40 calcined after drying. Here, too, drying is preferably carried out by spray drying. After calcination, the oxometalates B, B * can be comminuted again (for example by wet or dry milling, for example in a ball mill or by jet milling) and from the powder, which often consists of essentially 5 spherical particles, the grain size with a in the large diameter range desired for the multimetal oxide (I) according to the invention (in the 7

Rule> 0 to 200 μm, preferably 0.1 to 100 μm and particularly preferably 0.2 to 30 μm) by separation in a manner known per se (e.g. wet or dry sieving).

A preferred method of producing oxometalates B * of the general formula CuιSb _g H _h O _y consists in first dissolving antimony trioxide and / or Sb ₂ θ ₄ in an aqueous medium using hydrogen peroxide in a, preferably finely divided, Sb (V) compound, eg Sb (V ) Oxide hydroxide hydrate, to transfer the resulting aqueous suspension with Cu carbonate (which may have the composition Cu (OH) ₂ CO ₃ , for example), the introduced Cu carbonate by adding ammonia (for example as an aqueous solution) to solve, to dry the resulting aqueous mixture, for example spray-drying as described, and to calcine the powder obtained, if appropriate after subsequent kneading with water and subsequent extrusion and drying, as described. Of course, the ammonia required to dissolve the Cu carbonate can also be added partially and / or completely before or together with the introduction of the Cu carbonate.

In the case of oxometalates B different from oxometalates B *, it proves to be particularly advantageous to start from an aqueous antimony trioxide suspension and to dissolve the X ⁶ elements therein as nitrate and / or acetate, to spray-dry the resulting aqueous mixture as described and then to do so calcine the resulting powder as described.

In a corresponding manner, the elementary constituents of the oxometalates A,

Mo _i2 X _a X x Xd S _e x | 0 _Xf

produces a finely divided, intimate dry mixture which, however, is usually not precalcined (starting mass 2). If the initial mass 2 is pre-calcined, the calcination is expediently carried out at 150 to 450 ° C (under inert gas or inert gas with oxygen, e.g. air).

Particularly suitable starting compounds are:

W ammonium paratungstate,

Mo ammonium heptamolybdate,

V ammonium metavanadate,

P 70 to 100 wt. -%, preferably 76 to 85 wt. -% phosphoric acid, 8th

Sb: Senarmontite,

S: ammonium sulfate,

Re: rhenium pentoxide or ammonium perrhenate,

B: boric acid, As: arsenic trioxide,

Si: water glass,

Nb: ammonium nioboxalate or ammonium niobate,

Alkali metals: alkali metal nitrates,

NH ₄ : ammonium sulfate, nitrate or carbonate, Bi: bismuth nitrate,

Cu: copper nitrate.

The starting mass 1 and the starting mass 2 are then mixed with one another in the desired quantitative ratio, wet or dry (preferably dry), the mixture is shaped and then calcined at temperatures from 150 to 450 ° C. for several hours. The calcination can be carried out under inert gas, but also under a mixture of inert gas and oxygen, e.g. Air. Forming the mixture of starting mass 1 and starting mass 2 can e.g. by compression (e.g. tabletting, extrusion or extrusion), whereby lubricants such as graphite or stearic acid as well as molding aids and reinforcing agents such as microfibers made of glass, asbestos, silicon carbide or potassium titanate can be added. In the case of full catalysts, the compression takes place immediately to the desired catalyst geometry, hollow cylinders with an outer diameter and a length of 2 to 10 mm and a wall thickness of 1 to 3 mm being preferred as such. In general, the mixture of the starting mass 1 and the starting mass 2 can be formed both before and after the calcination. This can e.g. also be carried out in such a way that the mixture is comminuted after the calcination and applied to inert supports for the preparation of coated catalysts. The application can also take place before the final calcination. In this case, the application is preferably carried out in accordance with EP-B 293 859. Of course, the multimetal oxide compositions (I) according to the invention can also be used in powder form.

The multimetal oxide compositions (I) according to the invention are particularly suitable as catalysts with increased selectivity for a given conversion and increased activity for the gas-phase catalytically oxidative production of methacrylic acid from methacrolein. 9

The catalytic gas phase oxidation of methacrolein to methacrylic acid using the catalysts according to the invention can be carried out in a manner known per se, e.g. shown in DE-A 40 22 212, done.

The same applies to the separation of methacrylic acid from the product gas flow. The oxidizing agent oxygen can e.g. in the form of air, but also in pure form.

Because of the high heat of reaction, the reactants are preferably diluted with inert gas such as N ₂ , CO ₂ , saturated hydrocarbons and / or with water vapor.

In the case of a methacrolein: oxygen: water vapor: inert gas ratio of 1: (1 to 3): (2 to 20): (3 to 30), particularly preferably 1: (1 to 3): (3 to 10 ): (7 to 18) worked. The methacrolein used can have been obtained in various ways, e.g. by gas phase oxidation of isobutene, tert. -Butanol or the methyl ether of tert-butanol. It is advantageous to use methacrolein, which can be obtained by condensation of propanol with formaldehyde in the presence of secondary amines and acids in the liquid phase in accordance with the processes described in DE-PS 875 114 or DE-AS 28 55 514. The gas phase oxidation can be carried out both in fluidized bed reactors and in fixed bed reactors. It is preferably carried out in tube bundle reactors in the tubes of which the catalyst mass, preferably in the form of cylindrically shaped particles, is fixedly arranged. The reaction temperature is usually 250 to 350 ° C, the reaction pressure is usually in the range of 1 to 3 bar and the total space load is preferably 800 to 1800 Nl / l / h. Under these conditions, the methacrolein conversion in a single reactor pass is usually 60 to 90 mol%. Interestingly, the compositions according to the invention retain their properties essentially unchanged over an extended period of operation.

In the process described, however, it is usually not pure methacrylic acid that is obtained, but a product mixture from which the methacrylic acid must subsequently be separated.

This can be carried out in a manner known per se, for example by washing the reaction gases with water after indirect and / or direct cooling at from 40 to 80 ° C., an aqueous methacrylic acid solution being obtained from which the methacrylic acid is usually extracted by an organic Solution - 10 medium removed and separated from the same by distillation.

In addition to the gas phase catalytic oxidation of methacrolein to methacrylic acid, the compositions I according to the invention are also able to catalyze the gas phase catalytic oxidation and ammoxidation of other saturated, unsaturated and aromatic hydrocarbons, alcohols, aldehydes and amines.

The gas-phase catalytic oxidation of other alkanes, alkanols, alkanals, alkenes and alkenols (eg propylene, acrolein, tert-butanol, methyl ether of tert-butanol, isobutene, isobutane or isobutyraldehyde) to olefinically unsaturated aldehydes and / or carboxylic acids and the corresponding nitriles (ammoxidation, especially from propene to acrylonitrile and from isobutene or tert-butanol to methacrylonitrile). Particular emphasis should be given to the production of acrylic acid, acrolein and methacrolein, as well as the oxidation of n-butane to maleic anhydride and that of butadiene to furan. However, they are also suitable for the oxidative dehydrogenation of organic compounds.

Unless otherwise stated, turnover, selectivity and retention time are defined in this document as follows:

τUiπmsr, a _{^ *} t-zr, τUi a ₌ "n - number of moles of converted methacrolein _x 100

Methacrolein (%) number of moles of methacrolein used

Mole number of methacrolein implemented

Selectivity S der (%) ₌ to methacrylic acid _{χ 10Q}

Methacrylic acid formation Total number of moles of methacrolein implemented

filled with catalyst

Empty volume of the reactor (1)

Dwell time (sec) = x 3600 synthesis gas throughput (Nl / h)

Examples

I) Production of starting materials

a) Production of a starting mass 2

With stirring, 1086 g of (H ₄ ) ₆ MoO ₂ * 4H ₂ 0 were dissolved in ₆ l of water heated to 60 to 65 ° C. Then 132.2 g of a 76 wt. -% aqueous 11

H ₃ PO ₄ solution and then 61 g NHV0 ₃ added. An aqueous solution 1 was obtained. In parallel, 199.9 g of CsNO _{3 were dissolved} in 600 ml of water and 104.4 g of an aqueous copper nitrate solution (15.5% by weight of Cu) were diluted with 212 ml of water and then both solutions in the above Order of solution 1 dropped (within 20 min). The resulting aqueous mixture was spray-dried at an outlet temperature of 120 ° C. (inlet temperature = 350 ° C.). The resulting starting mass 2 had the following stoichiometry:

CSι, ₉₉ CUo, 5P2 θι ₂ Vι, o2θχ.

b) Preparation of a comparative starting mass 1 (a)

With stirring, 880 g of Sb ₂ 0 ₃ with an Sb content of 83% by weight (= 6 mol Sb) were suspended in 4 1 of water. A solution of 724.8 g of Cu (N0 ₃ ) _* 3H ₂ 0 (3 3 mol Cu) in 4 l of water was then added to the aqueous suspension. The resulting aqueous mixture was stirred at 80 ° C. for 2 h and then spray-dried (inlet temperature = 350 ° C., outlet temperature = 110 ° C.).

About 150 g of the spray powder obtained were passed through 20 Nl / h in a rotary tube oven (internal volume = 1 1)

Air is gradually heated up to 150 ° C within 1 h, then to 200 ° C within 4 h, then to 300 ° C within 2 h and finally to 400 ° C within 2 h. The powder was then heated to 900 ° C. in the course of 48 h while passing 20 l / h of air and finally cooled to room temperature. The resulting comparison starting mass had the stoichiometry CuSb ₂ Og.

c) Preparation of a starting mass l (a)

With stirring, 880 g of Sb ₂ 0 ₃ with an Sb content of 83% by weight (= 6 mol Sb) were suspended in 4 1 of water. Then 765 g of a 30 wt. -% aqueous H ₂ 0 solution (= 6.75 mol H ₂ 0) added. The aqueous mixture was then heated to 100 ° C. in the course of 1 h and stirred at this temperature for 5 h under reflux. A solution of 724.8 g of Cu (N0 ₃ ) ₂ * 3 H ₂ 0 (= 3 mol of Cu) in 4 l of water was then added to the aqueous suspension over the course of 30 minutes, the temperature of the suspension dropping to 60 ° C. . 407.9 g of an aqueous ammonia solution (25% by weight of NH ₃ = 6 mol of NH ₃ ) were then added at this temperature. Then 12, the aqueous suspension was stirred at 80 ° C. for 2 h and then cooled to 25 ° C. Finally, the aqueous suspension was spray dried (inlet temperature = 350 ° C, outlet temperature = 110 ° C). In a rotary kiln (internal volume = 1 1), approx. 150 g of the spray powder obtained was passed in stages while passing 20 Nl / h of air first to 150 ° C. within 1 h, then to 200 ° C. within 4 h, then within 2 h to 300 ° C and finally heated to 800 ° C within 2 h. The latter temperature was maintained for 2 hours and then cooled to room temperature. The resulting comparison starting mass had the stoichiometry CuSb ₂ 0 ₆ .

d) Production of a comparative starting mass 1 (b) Like the production of the starting mass 1 (a), but without the use of H0.

e) production of a starting mass l (b)

With stirring, 880 g of Sb ₂ θ ₃ with an Sb content of

83% by weight (= 6 mol Sb) suspended in 4 l of water. Then 765 g of a 30 wt. -% aqueous H ₂ 0 ₂ solution (= 6.75 mol H ₂ 0 ₂ ) added. The aqueous mixture was then heated to 100 ° C. in the course of 1 hour with stirring and stirred at this temperature for 5 hours under reflux. A solution of 595.6 g of Cu (CH ₃ C00) ₂ * H ₂ O (Cu content = 32% by weight) (Ä 3 mol Cu)) in 4 l of water was then added to the aqueous suspension within 30 minutes , the temperature of the suspension dropping to 60 ° C. 407.9 g of an aqueous ammonia solution (25% by weight of NH ₃ = 6 mol of NH ₃ ) were then added at this temperature. The aqueous suspension was then stirred at 80 ° C. for 2 h and then cooled to 25 ° C. Finally, the aqueous suspension was spray-dried (inlet temperature = 350 ° C, outlet temperature = 110 ° C).

In a rotary kiln (internal volume = 1 1), approx. 150 g of the spray powder obtained was passed in stages while passing 20 Nl / h of air first to 150 ° C. within 1 h, then to 200 ° C. within 4 h, then within 2 h to 300 ° C and finally heated to 800 ° C within 2 h. The latter temperature was maintained for 2 hours and then cooled to room temperature. The resulting reference mass had the stoichiometry CuSb ₂ θ ₆ . 13

II) Manufacture of multimetal oxide catalysts

a) Comparative catalyst 1

The starting mass 2 was mixed with 2% by weight of graphite and tabletted into hollow cylinders (7 mm × 5 mm × 3 mm = length × outer diameter × inner diameter). The hollow cylinders were calcined in an air-circulating air oven as follows (500 Nl / h air per kg hollow cylinder): First, starting from 25 ° C, the heating rate was 4 ° C / h to 270 ° C. The temperature was then increased to 400 ° C. at a heating rate of 2 ° C./h and this temperature was maintained for 5 hours.

b) Comparative catalyst 2

617.2 g of starting mass 2 were mixed with 54 g of comparative starting mass 1 (a). Then 2% by weight of graphite was added and the resulting mass was tableted into hollow cylinders (7 mm × 5 mm × 3 mm = length × outer diameter × inner diameter). These were calcined as under Ha).

c) Multi-metal oxide catalyst according to the invention a)

Like Ilb), but 54 g of the starting mass 1 (a) were used instead of the comparative starting mass 1 (a).

d) Comparative catalyst 3

Like Ilb), but 54 g of comparative starting mass 1 (b) were used instead of comparative starting mass 1 (a).

e) Multi-metal oxide catalyst b)

Like Ilb), but 54 g of starting mass 1 (b) were used instead of comparative starting mass 1 (a).

III) Use of the multimetal oxide catalysts from II) for the gas phase oxidation of methacrolein to methacrylic acid

The catalysts were placed in a tubular reactor (10 mm inside diameter, 75 g catalyst bed, salt bath temperature) and at reaction temperatures in the range from 290 to 310 ° C. using a residence time of 3.6 seconds with a gaseous mixture of the composition 14

5% by volume methacrolein, 10% by volume oxygen, 30% by volume water vapor and 55% by volume nitrogen

loaded. The salt bath temperature was adjusted in all cases so that a uniform methacrylic acid conversion U of about 63.0% resulted. A lower salt bath temperature shows an increased catalyst activity. The product gas mixture flowing out of the tubular reactor was analyzed by gas chromatography. The results for the selectivity S of methacrylic acid formation using the various catalysts are shown in the table below.

table

Salt bath U (mol%) S (mol%) temperature (° C)

Comparative - 308 61.5 80.3 catalyst 1

Comparative - 299 64.0 83.2 catalyst 2

Invention catalyst 293 63.1 88.4 a)

Comparative - 298 64.0 81.0 catalyst 3

Invention 292 63.7 89.1 catalyst b)

Claims

15 patent claims

1. Multimetal oxide compositions of the general formula I

[A] _p [B] _q (I),

in which the variables have the following meaning:

A = Mθχ Xa bc Xd S _e Xf O _x ,

B = Xi Sbg H _h O _y ,

X ¹ = phosphorus, arsenic, boron, germanium, and / or silicon,

X ² = vanadium, niobium, tungsten, rhenium and / or rhodium,

X ³ = lithium, sodium, potassium, rubidium, cesium, silver and / or copper,

X ⁴ = antimony and / or bismuth,

X ⁵ = hydrogen and / or NH ₄ ®,

X ⁶ = copper, zinc, cobalt, iron, cadmium, manganese, magnesium, calcium, strontium and / or barium,

a = 1 to 6,

b = 0 to 6,

c = 0 to 5,

d = 0 to 6,

e = 0 to 3,

f = 0 to 20,

g = 0.1 to 50,

h = 0 to 50, 16 x, y = numbers determined by the valency and frequency of the elements other than oxygen in (I) and

p, q = non-zero numbers whose ratio p / q is 1: 0.01 to 1: 5,

that the portion [A] _p in the form of three-dimensionally extended areas A of the chemical composition

A: Mθ _i2 X _a Xb Xc XS _e Xf O _x

B Xi Sbg H _h Oy

contain, areas A, B being distributed relative to one another as in a finely divided mixture of A and B,

with the proviso that to produce the multimetal oxide compositions (I) at least one separately preformed oxometalate B,

Xi Sbg H _h Oy,

is used, which is obtainable by preparing a dry mixture from sources of the elemental constituents of oxometalate B, which contain at least part of the antimony in the oxidation state + 5, and calcining this at temperatures from 200 to 1200 ° C.

2. A process for the preparation of multimetal oxide compositions according to claim 1, in which an oxometalate B,

X _l Sb _g H _h Oy,

preformed in finely divided form and then with sources of the elementary constituents of the multimetal oxide mass A, 17

MO12 Xa ¹ Xb c Xd S _e Xf O _x ,

processed in the desired ratio to a dry mixture and calcined at a temperature of 150 to 450 ° C, characterized in that at least a portion of the oxometalate B can be obtained by using sources of the elemental constituents of the oxometalate B, the at least one Part of the antimony in the oxidation level +5, produces a dry mixture and calcined it at temperatures from 200 to 1200 ° C.

3. Process of the gas-phase catalytic oxidative production of methacrylic acid from methacrolein, characterized in that a multimetal oxide according to claim 1 is used as the catalyst.